Macrophages cultured for several days with mediators from stimulated sensitized lymphocytes are found to display a number of activated functions, such as increased adherence to surfaces, increased phagocytosis and increased killing of tumor cells. Study of the biochemical changes which occur in macrophages at early times after addition of lymphocyte mediators is of great importance for the understanding of the late functional changes. Since the cell surface is important in several of the activated functions, e.g., recognition of tumor cells, the purification of plasma membranes from macrophages is being undertaken. This involves cell homogenization and the techniques of sucrose density centrifugation. Various sensitive radioactive and photometric assays are used to characterize the plasma membrane fraction and to monitor the fractionation of other subcellular particles. The procedure for purifying plasma membranes will allow, among other things, the comparison of the glycoprotein composition of plasma membranes from mediator activated macrophages and from control macrophages. This involves disc gel electrophoresis and radioactive techniques. Further studies using radioimmunoassay will examine whether lymphocyte mediators cause an early change in the cyclic GMP levels of macrophages. It is known that prostaglandins can influence macrophage functions and that protaglandins are present at sites of inflammation. Using radioimmunoassay and cell culture techniques, I will examine whether lymphocyte mediators influence the synthesis of prostaglandins by macrophages.